Physics…'Nuff Said

Completing the Rube Goldberg Machine!

After a week or two of rigorous (and agonizing) attempts at getting a successful run at the Rube Goldberg machine, we have finally done it! With a total of 16 different simple machines, the task of pouring a cup of Kool-Aid is accomplished. This blog post shows the machine, and gives an analytical description of each component.

Here is an explanation of the machine at work:

Individual Machine Analysis:

Machine #1 (Water Hose) –
Our first machine involved the turning on of a water faucet, and the progression of water through a tube. A relatively simple way to start the machine. It is worth noting that the water pressure exerted from the faucet is greater than the pull of gravity, which allows the water to travel upwards through our loops of tubing. (It’s not everyday you see water run UP hill, do you?)

Machine #2 (Pulley System) –
The water from the first machine let out into a container. This container was attached to a pulley system, with a block of wood on the other side. In the beginning, the weight of the block exceeded the weight of the plastic container. However, as the water filled the container, the weight shifted. The end result was the block being lifted. This machine demonstrates how pulleys allow an object to be lifted rather easily. The string started with full tension on the block side. As the water filled the container, the tension started to balance out, and then continued to shift, until full tension was on the container side. By spreading out this tension across pulleys, it becomes easier to lift objects.

Machine #3 (Car on Ramp) –
The third machine came in the form of a car on a ramp. The ramp was tilted; the car barred by the wooden block. When the block was removed, gravity took hold of the car, and moved it down the track. The car then knocked a weight off the table. This machine is best for observing Newton’s Laws of Motions, especially the third one. Though our video doesn’t show it, the car recoiled backwards when it impacts the weight. This is due to the idea that every action has an equal and opposite reaction. Furthermore, the second law can be derived from this machine. Simply put, the force the car exerts is in the same direction that the car is accelerating (due to gravity). Direction is an important part of vectors, which is what the second law is all about.

Machine #4 (Trigger Pull) –
This machine is simple: the weight, falling off the table, pulls the trigger of a Nerf Gun. For this component, we used gravity to assist us (any object falling under the force of gravity only is known to be in free fall, by the way). The weight was one kilogram. We found through experimentation that this was heavy enough to cause a seemingly instantaneous tug on the string. As far as the Physics itself, the concept is simple: heavier objects fall with a greater force (please note that force and acceleration are two different things. All objects fall at the same rate of speed).

Machine #5 (Dart Shoots Hinge) –
The next machine involves the dart from the Nerf Gun hitting a “plate”, which is connected to a hinge. The hinge, which is positioned upright, falls downward onto the next step. For this, we relied on the idea that kinetic energy is transferred during collision. This idea goes hand in hand with the conservation of energy idea: the energy of the dart is not lost; rather, it transfers itself to the hinge, causing it to move.

Machine #6 (Death Car Down Track) –
The hinge would fall down into machine six, which would be pushing Death Car down a track. Death Car, so you know, is a hot wheels car with a razor blade attached to one end, and a small stir stick protruding out the other. The energy from the hinge (which, in turn, came from the dart) would be transferred to the car. The stir stick is what actually made contact with the hinge. We ensured the stick was incredibly rigid, because then the energy from the hinge would make the entire car “bounce”; dislodging itself from its place of resting. Also, Death Car started out with a large amount of potential energy: it was sitting in a high place. After we hit it, however, gravity started to take hold, and the potential energy converted to kinetic energy. We used this kinetic energy as a means of activating our next machine.

It is also worth mentioning that this machine helped us demonstrate inertia. If our car went down the track too fast (or if the track was too steep), then the car would fly off-course. This demonstrates the idea that an object in motion will continue to stay in motion. We had to ensure that our car was moving slow enough to allow gravity to dominate, and keep the car firmly on the track.

Machine #7 (Cutting String) –
As Death Car made its way down the track, it accelerated and gained momentum. At the end of the track was a balloon tethered to a thin string, right in the path of Death Car. The force of the razor blade’s inertia against the fibers of the string would cause shearing. The razor would hit the hard sheet metal we had braced to intercept it, sandwiching the soft string between two hard objects with great force. The energy that started with the air pressure to shoot a Nerf dart moved transferred from our hinge, now ends up dissipating as Death Car ends at the bottom of the track. However, the balloon whose string Death Car cuts continues the machine with it’s own momentum…

Machine #8 (Balloon Nudges Wood) –
The rising balloon would hit a small wooden stick hanging off the table. At the other end of the stick lies a small piece of Hotwheels track with a ball bearing attached. The stick functions as a first class lever, the edge of the table acting as the fulcrum, the upward force of the balloon adding effort to the system, and the track and ball bearing being the load. It’s worth noting that our lever behaved very strangely; the upward motion of the balloon sent the ball bearing moving downward, but since it was braced against the table, the only observable motion was a tiny nudge of the ball bearing. But this nudge is exactly what the machine was designed to create, since it would give the bearing enough motion to dislodge itself from the track.

Machine #9 (Ball Dislodges) –
The force of the lever causes motion on the Hotwheels track and the ball bearing resting on it. This side of the lever was elevated in order to let the stick’s downward motion have a greater effect on the track. The force of the balloon leaves the machine, and the force of gravity on the ball is what would move us forward from here.

Machine #10 (Ferris Wheel) –
The ball bearing would fall off the track and enter a long PVC tube. The tube opens out on a Ferris Wheel made of K’nex pieces. Taped to the wheel is a small plastic cup. The wheel is kept from spinning by a small wooden stick pressed against one of its spokes. The friction between the stick and the wheel keeps anything from moving, unless a force is applied downward on the wheel. The ball bearing lands in the cup and imparts its inertia onto the wheel. This impact allows the wheel to overcome the friction of the stick, and begin moving downward in the direction corresponding to the ball bearing. The circular momentum of the Ferris Wheel keeps it turning around the axle it’s bound to at the center, so the small force of the ball is enough to get the wheel turning.

Machine #11 (Baseball Rolls) –
Prior to the introduction of the ball bearing, a baseball would be sitting at the top of the Ferris wheel, balanced between it’s two top spokes. At its elevated position it has plenty of potential energy the machine can use. Once the wheel spins far enough so that what were once its top spokes begin facing downward, the baseball now feels the force of gravity on a inclined slope rather than a wedge. This change in position allows the ball the roll off the Ferris wheel, ready to impart the kinetic energy it gained from gravity to the next part of the machine.

Machine #12 (Target Practice) –
The baseball falls on and transfers its energy to our next contraption. It is a vertical metal rod with a supportive base to keep it upright. Attached to the middle of the rod is a yardstick. The yardstick is screwed loosely into the rod at its centerpoint, so it can function as a radial lever (if effort is applied up or down on one end, the yardstick will spin around the point it is screwed in at). The yardstick is tilted at about 70 degrees upward, the higher end facing the Ferris Wheel. Taped to the elevated end is a circular “target” of sorts. The baseball lands on this target, imparting its energy downwards onto the lever and making it spin…

Machine #13 (The Domino Effect) –
The next part of the machine is the perfect illustration of the Law of Conservation of Energy. The lever begins spinning as a result of energy the baseball provided it. As the lever spins, one end of the yardstick hits a domino with upward force. This causes the domino to tip over, transferring the energy it received from the lever to another domino in its path. As you may be able to guess, there is a long line of dominoes in front of the lever, waiting to be knocked over. In this way kinetic energy moves horizontally along the line of dominoes, each one forming a link in the chain. So, the potential energy of the elevated baseball, which became gravitational mechanical energy, traveled all the way across the room, into the machine at the end of the line of dominoes.

Machine #14 (Mouse-Trap Magic) –
The final domino in the sequence tips over and lands on an armed mouse trap. The metal lever of the trap is attached to a string, which goes from the trap on the floor, up to a small, upright piece of wood on a table. The wood is supporting a tray of marbles, which we’ll discuss later. As the domino hits the trap, the potential energy of the tension within the trap is release, and the metal lever snaps downward. The force of the snapping, as well as the few inches of movement the lever exhibits, pulls on the already taught string connected to the wooden stick, forcing the stick itself to move…

Machine #15 (Running of the Marbles) –
As stated earlier, the mouse trap is connected to a tray lined with marbles. Many marbles. Lots and lots of marbles. I don’t think you understand…SO MANY marbles (or at least it seemed that way when they all spilled)…

Anyway, the activation of the mouse trap caused the wood supporting the front of the tray (the back was elevated with books) to fall two or three inches. This is enough of an incline for the marbles to roll off the tray and down an extremely large track. This machine once again shows us the law of inertia. The removal of the wood piece was sudden enough that – for a split second (unseeable on the video) – the tray remained elevated (an object at rest stays at rest). Only when gravity “took hold” did the tray fall. It is the same concept as the pulling off of a table cloth without disturbing the plates on top of it. We know this occurred because, if the wooden piece was removed any slower, the tray would buckle, tilt, or do anything but fall straight; it would be moved with the wooden piece. The rest of the machine is merely gravity at work (gravity is what turns the potential energy of the marbles into kinetic energy). The marbles gained momentum as they rolled down the track: you can see this in the video when the marbles turn the corner and some “jump” out; a product of the energy in the marble experiencing the sudden stop that is the corner. It is this momentum that helped us give our next machine a little extra “umph”.

Machine #16 (Kool-Aid Dispensary) –
The last machine in our contraption involved a bag resting above a syringe, which in-turn was resting above a cup. The marbles from the previous step would be funneled into the bag. The accumulated weight from the marbles, thanks once again to our friend gravity, was enough to push the syringe downward – thereby filling our cup with Kool-Aid. We analyzed the workings of a syringe when it came time to apply the scientific, analytical perspective to our machine. When you fill a syringe with a substance, in our case Kool Aid, the substance exerts a force on every wall of the syringe. The amount of force is dependent upon temperature and pressure (the latter, of course, is obtained by changing volume). The external force pushing on the syringe, which is air, is not greater than the force that the Kool Aid is pushing back. Therefore, the syringe doesn’t compress on its own. But, by adding the weight of a bunch of marbles, the external force becomes greater than the internal force that the liquid is pushing the syringe back with. This results in the Kool Aid leaving the syringe. Who knew such a simple device could have so much physics behind it?

When all the components listed above come together, they create a (rather impressive, if we do say so ourselves) working Rube Goldberg Machine! Here is a video showing each step activating in succession during one run through. In short: here is a video of our success! It finally worked! Enjoy!